The present invention relates to ink jet printers, and more particularly, to printing systems which employ off axis ink supplies connected to a carriage mounted printhead via tubing.
Ink jet printers are well known in the art, and many utilize a carriage which carries one or more ink jet cartridges. These carriages typically carry the printheads in a traversing or scanning movement, transverse to the printer paper path. It is also well known to provide an external stationary ink reservoir connected to the scanning cartridge via a tube. The external reservoir is typically known as an xe2x80x9coff axisxe2x80x9d ink reservoir. While providing increased ink capacity, these off axis systems present a number of problems. One problem is that of vapor losses from the tubing and air diffusion into the tubing system. A tube material that has been used is LDFE (low density polyethylene), since it is a low modulus material which is easy to bend. This low modulus material suffers from relatively high vapor losses and air diffusion into the tube. As a result of the vapor losses, the ink can change properties, degrading print quality and eventually causing tube or printhead clogging. Another problem with air diffusion into the tubing is that the printhead can ingest this air as ink is drawn from the external reservoir. As a result of air ingestion, the printhead can fill with air. During thermal fluctuations, the air can expand, causing printhead drool.
Another problem relating to printhead air ingestion is that this ingested air in the printhead can cause printhead starvation. Printhead starvation results when air enters a bubble chamber and displace ink, reducing the ink volume in the bubble chamber. As a heating element is heated to form a vapor bubble to eject ink from the bubble chamber the volume of ink ejected is reduced by the air in the chamber, reducing the quality of the output image. In addition, the reduced volume of ink ejected reduces the cooling of the heating element tending to reduce the lifetime of the printhead.
Air enters the tube connecting the reservoir with the printhead in two predominant ways. The first is air from the external reservoir can enter the tube. Air enters the external reservoir either through diffusion into this reservoir or during the filling process of the external reservoir air may become entrapped within the reservoir. As ink is drawn from the external reservoir the entrapped air within the reservoir is drawn into the tube. A second way in which air enters the tube is through diffusion of air from outside of the tube to the inside of the tube. Once air is present within the tube any increases in air within the tube produces an increase in the diffusion rate of air through the tube material, further exacerbating the problem of air ingestion in the printhead.
U.S. Pat. No. 5,426,459 to Kaplinski, assigned to the assignee of the present invention, incorporated herein by reference discloses the use of a section of finely woven stainless steel mesh as a combined filter and air check valve for use in an xe2x80x9con axisxe2x80x9d type print cartridge. An on axis print cartridge makes use of a printhead which is integrated with an ink reservoir. Therefore, an external tube is not required to fluidly connect the printhead and the reservoir. The air check valve is provided in the fluid path between the printhead and the ink reservoir to prevent air bubbles from traveling from the printhead into the reservoir. The valve also serves the function of a filter to prevent particulate contaminants from flowing from the ink reservoir into the printhead and clogging the printhead nozzles. The Kaplinski reference deals with the problem of leakage of air bubbles into the ink reservoir which equalizes the pressure on the ink in the reservoir reducing the negative pressure which is required to prevent the printhead from drooling when the printhead is subject to minor shocks during handling or operation. The Kaplinski reference does not deal with an off axis type printing system and therefore does not recognize the problem of introduction of air into the printing system via an external ink supply or the problem of air diffusion into the tube connecting the external reservoir with the printhead.
There is an ever present need of techniques for preventing the introduction of air into the printhead via the external reservoir in off axis printing systems. This technique should be a reliable way of preventing air ingestion by the printhead which reduces the printhead life. In addition, this technique should be relatively inexpensive and well suited to the manufacturing environment to reduce manufacturing costs of both the external reservoir as well as the off axis printing system.
The present invention is an ink supply for use in an ink jet printing system of the type having an ink jet printhead spaced from the ink supply. The ink jet printing system has an ink conduit configured for connection to each of the printhead and the ink supply for providing ink to the ink jet printhead. The ink supply includes an ink container for storing ink and a fine mesh disposed in a fluid path between the ink container and the ink conduit. The fine mesh has a mesh opening size which does not permit air to pass therethrough under normal nominal air bubble pressure experienced by the ink jet printing system in normal usage and storage. In one preferred embodiment the mesh is a wire mesh having a mesh size in the range from 10 microns to 100 microns. In this preferred embodiment the mesh is positioned within the ink container.